to creep; to steal up; to draw near unnoticed
猫は獲物に忍び寄るのが得意だ。
Cats are skilled at creeping up on prey.
危険が少しずつ忍び寄ってきていた。
Danger was slowly and silently closing in.
背後から誰かが忍び寄ったことに気づかなかった。
I didn't notice someone had crept up behind me.